1. Field of the Invention
The present invention relates generally to a coupling joint for use with a variety of pipes such as steel pipes for the industrial use, and more particularly to an improvement of a coupling joint, which comprises a middle ring and a pair of clamp rings with an efficient clamping and sealing effect, which provides a joint with such an assured performance of fluid-tightness that it may well be adapted for use in a high pressure piping installation such as penstocks for a hydraulic power plant or the like.
2. Description of the Prior Art
The typical construction of a pipe joint as shown in FIG. 1 which is generally known in the art of pipe couplings for the industrial piping installation is such that there are provided a pair of annular rubber packings (b), one each installed onto the leading end of each of pipes set in alignment and closely opposed relationship with each other, a middle ring (c) of cylindrical shape mounted to rest in the middle position between the pair of rubber packings (b), and a pair of annular clamping rings (d), one each disposed adjacent the exterior or opposite end face of one of the paired rubber packing (b) to the side where the middle ring (c) rest in position, and that the coupling joint is secured to provide the effect of sealing at the adjacent pipe ends by tightening a plurality of bolts (e) and nuts (f) so as to draw the paired clamp rings (d), toward each other, so that the pair of rubber packings are caused to be squeezed in urging relationship against the sealing surfaces (c.sub.1) of the middle ring (c), which are formed in an inclined fashion at an oblique angle, and against the pair of clamp rings (d), accordingly.
With such a typical construction of the pipe coupling joint for the use as mentioned above, however, it can commonly not be relieved of such drawbacks in practice, as are described below.
Referring more specifically to FIG. 2, it is known that a rubber packing (b) has generally an outer circumferential portion having a cross-sectional shape which is deformed, when it is tightened between the sealing surfaces (c.sub.1) of the middle ring (c) and the clamping side face of the clamp ring (d), thus resulting in a possible expansion or bulging of the outer circumferential portion of the rubber packing (b) out of the circumferential gap existing between the vertical face (c.sub.2) of the middle ring (c) and the clamping face of the clamp ring (d). Such bulged portion (b.sub.1) would very possibly kill or spoil the intended effect of clamping with these clamping members, and would then bring a possibly irregular distribution of clamping effect from such improper struggling conditions into existance around the circumferential portion of the rubber packing (b). Under such undesired conditions in the settings of the coupling joint, there would naturally be brought about a lack of reliability in the seals between the middle ring (c) and the rubber packing (b), and between the rubber packing (b) and the steel pipe (a) when the coupling joint is set in position and clamped, which would eventually result in the limit in the practice of such pipe joints only to the application where the design pressure level of the fluid flowing in the inside of the steel pipe (a) is 10 kg/cm.sup.2 or less, and there is no chance in practice for these pipe joints to be used in a higher fluid pressure level application.
Furthermore, as it is impossible in practice to have the inner diameters of the middle ring (c) and the clamp ring (d) strickly coincide with the outer diameter of the steel pipe (a) in the manufacture thereof, it is inevitable that there exist a substantial gap between these elements when installed together, and as a consequence, it is therefore impossible in practice to prevent the tendency of the gap as formed between these elements at the upper or higher points of the steel pipe (a) from growing to be greater than that at the under or lower points of the steel pipe (a), since the middle ring (c) and clamp ring (d) would fall to contact immediately upon the outer circumference of the steel pipe (a) because of the weights of these elements when installed in position, thus naturally making it difficult to have an even distribution of sealing effect all around the circumference, particularly on the lower side of the steel pipe (a).
The present invention is essentially directed to the provision of a proper resolution to such inconveniences and difficulties in practice as outlined above and experienced in the use of the conventional pipe coupling joints which have not been attended with any proper countermeasures therefor, for affording an extensive use with the general piping installation inclusive of a high pressure application.